Ships of great bulk are commonly equipped with a diesel engine producing the energy necessary to drive the submerged transmission line and propeller. The diesel engine is permanently connected to the transmission line to drive the propeller turning at the same speed as the engine.
Moreover, it is known to mechanically couple, to the transmission line, a rotating electrical machine, which is capable of receiving electrical energy that it converts into mechanical energy in order to provide additional mechanical energy to drive the propeller.
According to another operating mode, the rotating machine is used as a generator to produce electrical energy from mechanical energy provided by the main heat engine.
The ship also includes a secondary electrical power house including at least one auxiliary internal heat engine coupled to an alternator able to convert the mechanical energy coming from the secondary engine into electrical energy, and possibly an energy recovery system on the exhaust gases from the main engine that powers another alternator. The secondary heat engine is preferably a four stroke high speed diesel engine, powered with MDO (Marine Diesel Oil) or natural gas (LNG) light diesel. The electrical energy supplied by the secondary power house can be used to drive the rotating machine mechanically coupled to the transmission line.
Ships equipped with such a propulsion chain allow optimized management of the energy supplied by the main engine and the secondary power house, in that the main engine can be used to supply electrical energy on board the ship and the secondary power house can be used to participate in the propulsion of the ship via the rotating machine, which contributes, in addition to the main heat engine, to driving the propeller.
However, such a propulsion chain can be oversized and polluting for the driving of the ship under certain circumstances, in particular upon entering and leaving ports, or when the ship is used at reduced speeds.
For these particular operating circumstances, it is known to provide, on the transmission line between the main heat engine and the rotating machines, releasable coupling means that make it possible to uncouple the main heat engine and only use the rotating machine for entering or leaving ports.